CN103780118A

CN103780118A - Resonant DC link three-level soft switching inverter circuit

Info

Publication number: CN103780118A
Application number: CN201310746526.XA
Authority: CN
Inventors: 王强
Original assignee: Liaoning Shihua University
Current assignee: Liaoning Shihua University
Priority date: 2013-12-30
Filing date: 2013-12-30
Publication date: 2014-05-07

Abstract

The invention discloses a resonant DC link three-level soft-switching inverter circuit, which has the characteristics of simple structure and convenient control. Inverter and three-phase resistive inductive load, the auxiliary resonant circuit includes four electrolytic capacitors with voltage divider, six auxiliary switches, six diodes, two resonant capacitors and two resonant inductors, three-level inverter When the main switch needs to switch, the terminal voltage of the resonant capacitor C _r ₁ drops to zero through the resonance between the resonant capacitor C _r ₁ and the resonant inductance L _r ₁ , or through the resonance between the resonant capacitor C _r ₂ and the resonant inductance L _r ₂ The resonance among them makes the terminal voltage of the resonant capacitor C _r ₂ drop to zero, so as to realize the zero-voltage switching of the main switch. The invention achieves the purpose of expanding the soft switching topology of the resonant DC link to the diode-clamped three-phase three-level inverter, reduces the number of auxiliary switching devices, reduces hardware costs, and is simpler to control.

Description

A resonant DC link three-level soft-switching inverter circuit

技术领域：Technical field:

本发明涉及电力电子技术领域，确切地说，它是一种谐振直流环节三电平软开关逆变电路。The invention relates to the technical field of power electronics, specifically, it is a resonant DC link three-level soft-switching inverter circuit.

背景技术：Background technique:

相比于传统的两电平逆变器，三电平逆变器具有降低功率器件电压应力、减小电磁干扰和输出电压谐波含量等优点，这一技术越来越多的应用在高压大功率场合。近年来，高压大功率三电平逆变器已成为电力电子领域研究的热点。三电平逆变器应用在高压大功率场合时，其开关器件所承受的阻断电压和流过的电流都比较大，随着开关频率的提高，三电平硬开关逆变器的开关损耗也会显著增加，使逆变器的效率大大降低。三电平逆变器工作在硬开关状态时，较高的电压变化率和电流变化率也将会产生严重的电磁干扰。Compared with the traditional two-level inverter, the three-level inverter has the advantages of reducing the voltage stress of power devices, reducing electromagnetic interference and output voltage harmonic content, etc. This technology is increasingly used in high-voltage large power occasions. In recent years, high-voltage and high-power three-level inverters have become a research hotspot in the field of power electronics. When the three-level inverter is used in high-voltage and high-power applications, the blocking voltage and current flowing through the switching devices are relatively large. With the increase of switching frequency, the switching loss of the three-level hard-switching inverter will also increase significantly, greatly reducing the efficiency of the inverter. When the three-level inverter works in the hard switching state, the high voltage change rate and current change rate will also cause serious electromagnetic interference.

为了解决三电平硬开关逆变器存在的诸多问题，软开关技术开始被应用到三电平逆变器中，主要是把两电平逆变器的软开关拓扑（谐振极型逆变器和谐振直流环节逆变器）拓展到三电平逆变器中。吴洪洋等人在《中国电机工程学报》2002年第22卷第10期上公开了“一种无源谐振极型三电平软开关逆变电路”，该电路中无辅助开关器件，相比于三电平硬开关逆变电路，只增加了电感、电容和二极管等无源器件，就可以有效降低开关损耗和提高效率，但是该软开关逆变器中的开关器件在关断时承受的电压高于三电平硬开关逆变器中的开关器件，增加了开关器件的电压应力。范子超等人在《电工技术学报》2006年第21卷第5期上公开了“一种辅助谐振变换极型三电平软开关逆变电路”，辅助电路的控制和逆变器的控制完全独立，主开关管软开关操作不受负载条件影响，谐振电感和主功率通路分离，容易引入到多电平电路等几大优点，成为高压大容量高频逆变器的最有希望的解决手段，但是该拓扑结构应用到三相三电平逆变器时，辅助开关器件多达12个，控制复杂，硬件成本相对较高。In order to solve many problems existing in three-level hard-switching inverters, soft-switching technology has been applied to three-level inverters. and resonant DC link inverters) are extended to three-level inverters. Wu Hongyang and others disclosed "a passive resonant pole type three-level soft-switching inverter circuit" in the "Chinese Journal of Electrical Engineering" 2002, Volume 22, No. 10. There is no auxiliary switching device in this circuit. Compared with The three-level hard-switching inverter circuit can effectively reduce switching loss and improve efficiency by only adding passive components such as inductors, capacitors, and diodes. Higher than the switching devices in the three-level hard-switching inverter, increasing the voltage stress of the switching devices. Fan Zichao and others disclosed "an auxiliary resonant conversion pole type three-level soft switching inverter circuit" in "Journal of Electrotechnical Society" 2006, Volume 21, Issue 5. The control of the auxiliary circuit and the control of the inverter are completely independent , the soft switching operation of the main switching tube is not affected by the load conditions, the resonant inductance is separated from the main power path, and it is easy to introduce into multi-level circuits. It has become the most promising solution for high-voltage, large-capacity, and high-frequency inverters. However, when this topology is applied to a three-phase three-level inverter, there are as many as 12 auxiliary switching devices, the control is complicated, and the hardware cost is relatively high.

发明内容Contents of the invention

目前，谐振直流环节软开关拓扑结构因为其结构简单、控制方便，已被广泛地应用在两电平逆变器中，研究人员提出多种谐振直流环节两电平软开关逆变器，推动了谐振直流环节软开关逆变器的发展。为了将谐振直流环节软开关拓扑结构拓展到二极管箝位型三相三电平逆变器中，本发明提供了一种具有对称辅助电路的谐振直流环节三相三电平软开关逆变电路。At present, the resonant DC-link soft-switching topology has been widely used in two-level inverters because of its simple structure and convenient control. Researchers have proposed a variety of resonant DC-link two-level soft-switching inverters, which have promoted Development of a resonant dc-link soft-switching inverter. In order to extend the resonant DC-link soft-switching topology to a diode-clamped three-phase three-level inverter, the invention provides a resonant DC-link three-phase three-level soft-switching inverter circuit with a symmetrical auxiliary circuit.

一种谐振直流环节三电平软开关逆变电路，它的主电路包括一个直流电源、一个二极管箝位型三相三电平脉宽调制逆变器和三相阻感性负载，直流电源可以是把交流电整流成直流电的整流电源或者是电池串并联产生的直流电源；二极管箝位型三相三电平脉宽调制逆变器把直流电转换为交流电；直流电源和二极管箝位型三相三电平脉宽调制逆变器之间的部分称为直流环节。其特征在于：在直流环节添加的辅助谐振电路中，包括四个具有分压作用的电解电容、六个辅助开关、六个二极管、两个谐振电容和两个谐振电感。在直流母线之间串联了四个电解电容C₁、C₂、C₃和C₄，辅助开关S_a1、S_a2、S_a3，S_a4、S_a5和S_a6分别反并联二极管D_a1、D_a2、D_a3，D_a4、D_a5和D_a6。二极管D_a1的阴极与直流母线的P1极相连，二极管D_a1的阳极与直流母线的P2极相连，开关器件S_a1的集电极与二极管D_a1的阴极相连，开关器件S_a1的发射极与二极管D_a1的阳极相连，开关器件S_a2的发射极与直流母线的P2极相连，二极管D_a2的阳极与开关器件S_a2的发射极相连，二极管D_a2的阴极与开关器件S_a2的集电极相连，开关器件S_a2的集电极与开关器件S_a3的集电极相连，二极管D_a3的阴极与开关器件S_a3的集电极相连，二极管D_a3的阳极与开关器件S_a3的发射极相连，S_a3的发射极与谐振电感L_r1的一端相连，谐振电感L_r1的另一端与电解电容C₂的正极相连，电解电容C₂的正极与电解电容C₁的负极相连，电解电容C₁的正极与直流母线的P1极相连；二极管D_a4的阴极与直流母线的N2极相连，二极管D_a4的阳极与直流母线的N1极相连，开关器件S_a4的集电极与二极管D_a4的阴极相连，开关器件S_a4的发射极与二极管D_a4的阳极相连，开关器件S_a6的发射极与直流母线的N2极相连，二极管D_a6的阳极与开关器件S_a6的发射极相连，二极管D_a6的阴极与开关器件S_a6的集电极相连，开关器件S_a6的集电极与开关器件S_a5的集电极相连，二极管D_a5的阴极与开关器件S_a5的集电极相连，二极管D_a5的阳极与开关器件S_a5的发射极相连，开关器件S_a5的发射极与谐振电感L_r2的一端相连，谐振电感L_r2的另一端与电解电容C₄的正极相连，电解电容C₄的正极与电解电容C₃的负极相连，电解电容C₃的正极与电解电容C₂的负极相连，电解电容C₄的负极与直流母线的N1极相连；谐振电容C_r1的一端与直流母线的P2极相连，谐振电容C_r1的另一端与谐振电容C_r2的一端相连，谐振电容C_r2的另一端与直流母线的N2极相连，谐振电容C_r1和谐振电容C_r2的连接点再与电解电容C₂和电解电容C₃的连接点相连。直流母线的P1极与直流电源的正极相连，直流母线的P2极与逆变桥的正端相连，直流母线的N1极与直流电源的负极相连，直流母线的N2极与逆变桥的负端相连。A resonant DC link three-level soft-switching inverter circuit, its main circuit includes a DC power supply, a diode-clamped three-phase three-level pulse width modulation inverter and a three-phase resistive inductive load, the DC power supply can be A rectified power supply that rectifies alternating current into direct current or a direct current power supply generated by series-parallel connection of batteries; a diode-clamped three-phase three-level pulse width modulation inverter converts direct current into alternating current; a direct current power supply and a diode-clamped three-phase three-power The section between the flat PWM inverters is called the DC link. It is characterized in that: the auxiliary resonant circuit added in the DC link includes four electrolytic capacitors with voltage dividing function, six auxiliary switches, six diodes, two resonant capacitors and two resonant inductances. Four electrolytic capacitors C ₁ , C ₂ , C ₃ and C ₄ are connected in series between the DC buses, and the auxiliary switches S _a1 , S _a2 , S _a3 , S _a4 , S _a5 and S _a6 are connected in antiparallel with diodes D _a1 , D _a2 , D _a3 , D _a4 , D _a5 and D _a6 . The cathode of the diode D _a1 is connected to the P1 pole of the DC bus, the anode of the diode D _a1 is connected to the P2 pole of the DC bus, the collector of the switching device S _a1 is connected to the cathode of the diode D _a1 , and the emitter of the switching device S _a1 is connected to the diode The anode of D _a1 is connected, the emitter of switching device S _a2 is connected with the P2 pole of the DC bus, the anode of diode D _a2 is connected with the emitter of switching device S _a2 , the cathode of diode D _a2 is connected with the collector of switching device S _a2 , the collector of switching device S _a2 is connected to the collector of switching device S _a3 , the cathode of diode D _a3 is connected to the collector of switching device S _{a3 , the anode of diode D a3} _is connected to the emitter of switching device S _a3 , S _a3 The emitter of the resonant inductor L _r1 is connected to one end, the other end of the resonant inductor L _r1 is connected to the positive pole of the electrolytic capacitor _C2 , the positive pole of the electrolytic capacitor _C2 is connected to the negative pole of the electrolytic capacitor _C1 , and the positive pole of the electrolytic capacitor C1 is connected to the negative pole of the electrolytic capacitor _C1 . The P1 pole of the DC bus is connected; the cathode of the diode D _a4 is connected with the N2 pole of the DC bus, the anode of the diode D _a4 is connected with the N1 pole of the DC bus, the collector of the switching device S _a4 is connected with the cathode of the diode D _a4 , and the switching device The emitter of S _a4 is connected to the anode of diode D _a4 , the emitter of switching device S _a6 is connected to the N2 pole of the DC bus, the anode of diode D _a6 is connected to the emitter of switching device S _a6 , the cathode of diode D _a6 is connected to the switch The collector of the device S _a6 is connected, the collector of the switching device S _a6 is connected to the collector of the switching device S _a5 , the cathode of the diode D _a5 is connected to the collector of the switching device S _a5 , the anode of the diode D _a5 is connected to the collector of the switching device S _a5 The emitter of the switching device S _a5 is connected to one end of the resonant inductance L _r2 , the other end of the resonant inductance L _r2 is connected to the positive pole of the electrolytic capacitor _C4 , and the positive pole of the electrolytic capacitor _C4 is connected to the negative pole of the electrolytic capacitor _C3 The positive pole of the electrolytic capacitor _C3 is connected to the negative pole of the electrolytic capacitor _C2 , the negative pole of the electrolytic capacitor _C4 is connected to the N1 pole of the DC bus; one end of the resonant capacitor C _r1 is connected to the P2 pole of the DC bus, and the resonant capacitor C _r1 The other end is connected to one end of the resonant capacitor C _r2 , the other end of the resonant capacitor C _r2 is connected to the N2 pole of the DC bus, and the connection point of the resonant capacitor C _r1 and the resonant capacitor C _r2 is connected to the electrolytic capacitor C ₂ and the electrolytic capacitor C ₃ The connection points are connected. The P1 pole of the DC bus is connected to the positive pole of the DC power supply, the P2 pole of the DC bus is connected to the positive terminal of the inverter bridge, the N1 pole of the DC bus is connected to the negative pole of the DC power supply, and the N2 pole of the DC bus is connected to the negative terminal of the inverter bridge connected.

当三电平逆变器的主开关需要切换时，通过谐振电容C_r1和谐振电感L_r1之间的谐振使谐振电容C_r1的端电压下降到零，或是通过谐振电容C_r2和谐振电感L_r2之间的谐振使谐振电容C_r2的端电压下降到零，来实现主开关的零电压切换。When the main switch of the three-level inverter needs to switch, the terminal voltage of the resonant capacitor C _r1 drops to zero through the resonance between the resonant capacitor C _r1 and the resonant inductance L _r1 , or through the resonant capacitor C _r2 and the resonant inductance The resonance between L _r2 makes the terminal voltage of the resonant capacitor C _r2 drop to zero, so as to realize the zero-voltage switching of the main switch.

本发明的的优点是：相比于谐振极型三相三电平软开关逆变器，辅助谐振电路中的器件较少；两组镜像对称的辅助谐振电路位于三相三电平逆变器的直流环节，为主开关提供零电压开关的条件；主开关器件承受的电压和电流应力不会因为增加了辅助电路而高于硬开关逆变器；逆变器的主开关器件和辅助开关器件都可以实现软开关。The advantages of the present invention are: compared with the resonant pole type three-phase three-level soft-switching inverter, there are fewer devices in the auxiliary resonant circuit; two sets of mirror-symmetrical auxiliary resonant circuits are located in the three-phase three-level inverter The DC link of the main switch provides zero-voltage switching conditions; the voltage and current stress of the main switching device will not be higher than that of the hard-switching inverter due to the addition of auxiliary circuits; the main switching device and auxiliary switching device of the inverter can realize soft switching.

附图说明：Description of drawings:

图1是本发明谐振直流环节三电平软开关逆变电路图。Fig. 1 is a circuit diagram of a three-level soft-switching inverter with a resonant DC link in the present invention.

图2是本发明谐振直流环节三电平软开关逆变电路的单相电路图；图2（a）是S₁、S₂开通、S₃、S₄关断时的单相电路图；图2（b）是S₂、S₃开通、S₁、S₄关断时的单相电路图；图2（c）是S₃、S₄开通、S₁、S₂关断时的单相电路图。Fig. 2 is a single-phase circuit diagram of the resonant DC link three-level soft-switching inverter circuit of the present invention; Fig. 2 (a) is a single-phase circuit diagram when S ₁ and S ₂ are turned on and S ₃ and S ₄ are turned off; Fig. 2 ( b) is the single-phase circuit diagram when S ₂ and S ₃ are on and S ₁ and S ₄ are off; Figure 2(c) is the single-phase circuit diagram when S ₃ and S ₄ are on and S ₁ and S ₂ are off.

图3是本发明逆变电路的特征工作波形图。Fig. 3 is a characteristic working waveform diagram of the inverter circuit of the present invention.

图4是本发明逆变电路的各工作模式等效电路图；图4（a）是模式1等效电路图，图4（b）是模式2等效电路图，图4（c）是模式3等效电路图，图4（d）是模式4等效电路图，图4（e）是模式5等效电路图，图4（f）是模式6等效电路图，图4（g）是模式7等效电路图，图4（h）是模式8等效电路图。Fig. 4 is the equivalent circuit diagram of each working mode of the inverter circuit of the present invention; Fig. 4 (a) is the equivalent circuit diagram of mode 1, Fig. 4 (b) is the equivalent circuit diagram of mode 2, and Fig. 4 (c) is the equivalent circuit diagram of mode 3 Circuit diagram, Figure 4(d) is the equivalent circuit diagram of mode 4, Figure 4(e) is the equivalent circuit diagram of mode 5, Figure 4(f) is the equivalent circuit diagram of mode 6, Figure 4(g) is the equivalent circuit diagram of mode 7, Figure 4(h) is the equivalent circuit diagram of Mode 8.

图5是实验波形图；图5（a）是谐振电容C_r1的端电压u_Cr1和谐振电流i_Lr1的实验波形，图5（b）是辅助开关S_a1开通和关断时的电压u_Sa1和电流i_Sa1的实验波形，图5（c）是辅助开关S_a2开通和关断时的电压u_Sa2和电流i_Sa2的实验波形，图5（d）是辅助开关S_a3开通和关断时的电压u_Sa3和电流i_Sa3的实验波形，图5（e）是软开关逆变器输出线电压u_ab的实验波形，图5（f）是软开关逆变器三相的相电流的实验波形。Figure 5 is the experimental waveform diagram; Figure 5(a) is the experimental waveform of the terminal voltage u _Cr1 of the resonant capacitor C _r1 and the resonant current i _Lr1 , and Figure 5(b) is the voltage u _Sa1 when the auxiliary switch S _a1 is turned on and off and current i _Sa1 experimental waveforms, Figure 5(c) is the experimental waveform of voltage u _Sa2 and current i _Sa2 when the auxiliary switch S _a2 is turned on and off, Figure 5(d) is the experimental waveform when the auxiliary switch S _a3 is turned on and off The experimental waveforms of voltage u _Sa3 and current i _Sa3 , Figure 5(e) is the experimental waveform of the soft-switching inverter output line voltage u _ab , Figure 5(f) is the experimental waveform of the three-phase phase current of the soft-switching inverter waveform.

具体实施方式：Detailed ways:

实施例1Example 1

一、电路结构1. Circuit structure

参照图1，一种新型谐振直流环节三相三电平二极管箝位型软开关逆变器主电路，它可用于三相交流电机的驱动。主电路包括：一个直流电源1，一个辅助谐振电路2（由镜像对称辅助谐振电路A和B组成），一个公知的二极管箝位型三相三电平脉宽调制逆变器3，一个三相阻感性负载4。本发明用于二极管箝位型三相三电平逆变器的谐振直流环节软开关辅助谐振电路在直流母线之间串联了四个电解电容C₁、C₂、C₃、C₄，辅助开关S_a1、S_a2、S_a3，S_a4、S_a5、S_a6分别反并联二极管D_a1、D_a2、D_a3，D_a4、D_a5、D_a6。二极管D_a1的阴极与直流母线的P1极相连，二极管D_a1的阳极与直流母线的P2极相连，开关器件S_a1的集电极与二极管D_a1的阴极相连，开关器件S_a1的发射极与二极管D_a1的阳极相连，开关器件S_a2的发射极与直流母线的P2极相连，二极管D_a2的阳极与开关器件S_a2的发射极相连，二极管D_a2的阴极与开关器件S_a2的集电极相连，开关器件S_a2的集电极与开关器件S_a3的集电极相连，二极管D_a3的阴极与开关器件S_a3的集电极相连，二极管D_a3的阳极与开关器件S_a3的发射极相连，S_a3的发射极与谐振电感L_r1的一端相连，谐振电感L_r1的另一端与电解电容C₂的正极相连，电解电容C₂的正极与电解电容C₁的负极相连，电解电容C₁的正极与直流母线的P1极相连；二极管D_a4的阴极与直流母线的N2极相连，二极管D_a4的阳极与直流母线的N1极相连，开关器件S_a4的集电极与二极管D_a4的阴极相连，开关器件S_a4的发射极与二极管D_a4的阳极相连，开关器件S_a6的发射极与直流母线的N2极相连，二极管D_a6的阳极与开关器件S_a6的发射极相连，二极管D_a6的阴极与开关器件S_a6的集电极相连，开关器件S_a6的集电极与开关器件S_a5的集电极相连，二极管D_a5的阴极与开关器件S_a5的集电极相连，二极管D_a5的阳极与开关器件S_a5的发射极相连，开关器件S_a5的发射极与谐振电感L_r2的一端相连，谐振电感L_r2的另一端与电解电容C₄的正极相连，电解电容C₄的正极与电解电容C₃的负极相连，电解电容C₃的正极与电解电容C₂的负极相连，电解电容C₄的负极与直流母线的N1极相连；谐振电容C_r1的一端与直流母线的P2极相连，谐振电容C_r1的另一端与谐振电容C_r2的一端相连，谐振电容C_r2的另一端与直流母线的N2极相连，谐振电容C_r1和谐振电容C_r2的连接点再与电解电容C₂和电解电容C₃的连接点相连。直流母线的P1极与直流电源的正极相连，直流母线的P2极与逆变桥的正端相连，直流母线的N1极与直流电源的负极相连，直流母线的N2极与逆变桥的负端相连。Referring to Figure 1, a new resonant DC link three-phase three-level diode-clamped soft-switching inverter main circuit can be used for driving three-phase AC motors. The main circuit includes: a DC power supply 1, an auxiliary resonant circuit 2 (composed of mirror symmetrical auxiliary resonant circuits A and B), a known diode-clamped three-phase three-level pulse width modulation inverter 3, a three-phase Resistive inductive load4. The resonant DC link soft switch auxiliary resonant circuit used in the diode-clamped three-phase three-level inverter of the present invention connects four electrolytic capacitors C ₁ , C ₂ , C ₃ , and C ₄ in series between the DC bus bars, and the auxiliary switch S _a1 , S _a2 , S _a3 , S _a4 , S _a5 , and S _a6 are connected in antiparallel with diodes D _a1 , D _a2 , D _a3 , D _a4 , D _a5 , and D _a6 respectively. The cathode of the diode D _a1 is connected to the P1 pole of the DC bus, the anode of the diode D _a1 is connected to the P2 pole of the DC bus, the collector of the switching device S _a1 is connected to the cathode of the diode D _a1 , and the emitter of the switching device S _a1 is connected to the diode The anode of D _a1 is connected, the emitter of switching device S _a2 is connected with the P2 pole of the DC bus, the anode of diode D _a2 is connected with the emitter of switching device S _a2 , the cathode of diode D _a2 is connected with the collector of switching device S _a2 , the collector of switching device S _a2 is connected to the collector of switching device S _a3 , the cathode of diode D _a3 is connected to the collector of switching device S _{a3 , the anode of diode D a3} _is connected to the emitter of switching device S _a3 , S _a3 The emitter of the resonant inductor L _r1 is connected to one end, the other end of the resonant inductor L _r1 is connected to the positive pole of the electrolytic capacitor _C2 , the positive pole of the electrolytic capacitor _C2 is connected to the negative pole of the electrolytic capacitor _C1 , and the positive pole of the electrolytic capacitor C1 is connected to the negative pole of the electrolytic capacitor _C1 . The P1 pole of the DC bus is connected; the cathode of the diode D _a4 is connected with the N2 pole of the DC bus, the anode of the diode D _a4 is connected with the N1 pole of the DC bus, the collector of the switching device S _a4 is connected with the cathode of the diode D _a4 , and the switching device The emitter of S _a4 is connected to the anode of diode D _a4 , the emitter of switching device S _a6 is connected to the N2 pole of the DC bus, the anode of diode D _a6 is connected to the emitter of switching device S _a6 , the cathode of diode D _a6 is connected to the switch The collector of the device S _a6 is connected, the collector of the switching device S _a6 is connected to the collector of the switching device S _a5 , the cathode of the diode D _a5 is connected to the collector of the switching device S _a5 , the anode of the diode D _a5 is connected to the collector of the switching device S _a5 The emitter of the switching device S _a5 is connected to one end of the resonant inductance L _r2 , the other end of the resonant inductance L _r2 is connected to the positive pole of the electrolytic capacitor _C4 , and the positive pole of the electrolytic capacitor _C4 is connected to the negative pole of the electrolytic capacitor _C3 The positive pole of the electrolytic capacitor _C3 is connected to the negative pole of the electrolytic capacitor _C2 , the negative pole of the electrolytic capacitor _C4 is connected to the N1 pole of the DC bus; one end of the resonant capacitor C _r1 is connected to the P2 pole of the DC bus, and the resonant capacitor C _r1 The other end is connected to one end of the resonant capacitor C _r2 , the other end of the resonant capacitor C _r2 is connected to the N2 pole of the DC bus, and the connection point of the resonant capacitor C _r1 and the resonant capacitor C _r2 is connected to the electrolytic capacitor C ₂ and the electrolytic capacitor C ₃ The connection points are connected. The P1 pole of the DC bus is connected to the positive pole of the DC power supply, the P2 pole of the DC bus is connected to the positive terminal of the inverter bridge, the N1 pole of the DC bus is connected to the negative pole of the DC power supply, and the N2 pole of the DC bus is connected to the negative terminal of the inverter bridge connected.

辅助电路A（B）包括电解电容C₁（C₃）和C₂（C₄），辅助开关器件S_a1（S_a4）、S_a2（S_a5）、S_a3（S_a6），及其反并联二极管D_a1（D_a4）、D_a2（D_a5）、D_a3（D_a6），谐振电容C_r1（C_r2）和谐振电感L_r1（L_r2）。在参数值方面，C₁=C₂=C₃=C₄，C_r1=C_r2，L_r1=L_r2，R_a=R_b=R_c，L_a=L_b=L_c。当三电平逆变器的主开关需要切换时，通过辅助谐振电路A（B）中的C_r1（C_r2）和L_r1（L_r2）之间的谐振使C_r1（C_r2）的端电压下降到零，实现主开关的零电压切换。为简化分析，做如下假设：1）器件均工作在理想状态；2）谐振电感远小于负载电感，逆变桥开关状态过渡瞬间的负载电流I₀恒定；3）电解电容值足够大，其端电压恒定，并均分直流电源电压。取逆变器的单相电路进行分析，三电平逆变器有三种开关状态组合，分别是（a）S₁、S₂开通，S₃、S₄关断；（b）S₂、S₃开通，S₁、S₄关断；（c）S₃、S₄开通，S₁、S₂关断。这三种开关状态下的电路工作状态分别对应图2(a)，图2(b)和图2(c)，其中u_Cr1，i_Lr1和I₀的正方向如图2所示，在开关状态a和b之间的换流过程中，辅助电路A工作；在开关状态b和c之间的换流过程中，辅助电路B工作。Auxiliary circuit A (B) includes electrolytic capacitors C ₁ (C ₃ ) and C ₂ (C ₄ ), auxiliary switching devices S _a1 (S _a4 ), S _a2 (S _a5 ), S _a3 (S _a6 ), and their inverse Diodes D _a1 (D _a4 ), D _a2 (D _a5 ), D _a3 (D _a6 ), resonant capacitor C _r1 (C _r2 ) and resonant inductance L _r1 (L _r2 ) are connected in parallel. In terms of parameter values, C ₁ =C ₂ =C ₃ =C ₄ , C _r1 =C _r2 , L _r1 =L _r2 , R _a =R _b =R _c , L _a =L _b =L _c . When the main switch of _the three _- _{level inverter needs to be switched, the terminal of C r1 (C r2} ₎ _is _made The voltage drops to zero, realizing zero-voltage switching of the main switch. In order to simplify the analysis, the following assumptions are made: 1) The devices are all working in an ideal state; 2) The resonant inductance is much smaller than the load inductance, and the load current I ₀ at the transition moment of the switching state of the inverter bridge is constant; 3) The value of the electrolytic capacitor is large enough that its terminal The voltage is constant and shares the DC supply voltage equally. Taking the single-phase circuit of the inverter for analysis, the three-level inverter has three switch state combinations, namely (a) S ₁ and S ₂ are on, S ₃ and S ₄ are off; (b) S ₂ , S ₃ is turned on, S ₁ and S ₄ are turned off; (c) S ₃ and S ₄ are turned on, and S ₁ and S ₂ are turned off. The working states of the circuit in these three switching states correspond to Fig. 2(a), Fig. 2(b) and Fig. 2(c) respectively, where the positive directions of u _Cr1 , i _Lr1 and I ₀ are shown in Fig. 2, and in the switch During the commutation process between states a and b, the auxiliary circuit A works; during the commutation process between switching states b and c, the auxiliary circuit B works.

二、工作原理2. Working principle

以开关状态b到开关状态a的换流过程为例，来分析电路的工作原理。在开关状态b到开关状态a的换流过程中，辅助电路A工作，辅助电路B不工作，电路的特征工作波形如图3所示。根据图3，该电路在一个开关周期内分为八个工作模式。各工作模式的等效电路如图4所示。Taking the commutation process from switching state b to switching state a as an example, the working principle of the circuit is analyzed. During the commutation process from switching state b to switching state a, auxiliary circuit A works and auxiliary circuit B does not work. The characteristic operating waveform of the circuit is shown in Figure 3. According to Fig. 3, the circuit is divided into eight working modes in one switching cycle. The equivalent circuit of each working mode is shown in Fig. 4 .

工作模式：Operating mode:

模式1(t-t₀)：初始状态，S₂、S₃开通，S₁、S₄关断，正向负载电流I₀通过D₁₃和S₂续流，逆变器工作于稳态。Mode 1 (tt ₀ ): In the initial state, S ₂ and S ₃ are turned on, S ₁ and S ₄ are turned off, the forward load current I ₀ continues to flow through D ₁₃ and S ₂ , and the inverter works in a steady state.

模式2(t₀-t₁)：在t₀时刻，关断S_a2，同时开通S_a3，因为在关断S_a2之前，流过S_a2的电流已经等于零，所以S_a2实现了零电流关断；在L_r1的作用下，降低了流过S_a3电流的上升率，所以S_a3实现了零电流开通。开通S_a3以后，L_r1承受的电压值为E/4，L_r1被充电，i_Lr1线性增大，在t₁时刻，当i_Lr1线性增大到I_b1时，模式2结束。S_a3开通瞬间的电流上升率为Mode 2 (t ₀ -t ₁ ): At time t ₀ , turn off S _a2 and turn on S _a3 at the same time, because before turning off S _a2 , the current flowing through S _a2 is already equal to zero, so S _a2 realizes zero current shutdown Off; under the action of L _r1 , the rate of rise of the current flowing through S _a3 is reduced, so S _a3 realizes zero current opening. After S _a3 is turned on, the voltage value of L _r1 is E/4, L _r1 is charged, and i _Lr1 increases linearly. At time _t1 , when i _Lr1 linearly increases to I _b1 , mode 2 ends. The current rising rate at the moment of S _a3 turning on

${\frac{{di di}_{Sa Sa 33}}{dt dt} | |}_{t t = = {t t}_{00}} = = \frac{E E.}{44 {L L}_{r r 11}}$

(1)(1)

本模式的持续的时间为The duration of this mode is

${T T}_{22} = = {t t}_{11} - - {t t}_{00} = = \frac{44 {L L}_{r r 11} {I I}_{b b 11}}{E E.}$

(2)(2)

模式3(t₁-t₂)：在t₁时刻，关断S_a1，在电容C_r1的作用下，降低了S_a1关断瞬间端电压的上升率，所以S_a1实现了零电压关断。S_a1关断以后，L_r1和C_r1开始谐振，L_r1被充电，C_r1放电。i_Lr1逐渐增大，u_Cr1逐渐减小。当u_Cr1减小到E/4时，i_Lr1增加到最大值，然后L_r1开始放电，i_Lr1开始减小，u_Cr1继续减小，在t₂时刻，当i_Lr1减小到I_b1，u_Cr1减小到零时，模式3结束。本模式中，i_Lr1和u_Cr1的表达式分别为Mode 3 (t ₁ -t ₂ ): at time t ₁ , S _a1 is turned off, and under the action of capacitor C _r1 , the rising rate of terminal voltage at the moment of S _a1 turning off is reduced, so S _a1 realizes zero-voltage turn-off . After S _a1 is turned off, L _r1 and C _r1 start to resonate, L _r1 is charged, and C _r1 discharges. i _Lr1 increases gradually, and u _Cr1 decreases gradually. When u _Cr1 decreases to E/4, i _Lr1 increases to the maximum value, then L _r1 starts to discharge, i _Lr1 begins to decrease, u _Cr1 continues to decrease, at time t ₂ , when i _Lr1 decreases to I _b1 , Mode 3 ends when u _Cr1 decreases to zero. In this mode, the expressions of i _Lr1 and u _Cr1 are respectively

${i i}_{Lr Lr 11} ((t t)) = = \frac{E E.}{44 {Z Z}_{r r 11}} sin sin [[{ω ω}_{r r 11} ((t t - - {t t}_{11}))]] + + {I I}_{b b 11} cos cos [[{ω ω}_{r r 11} ((t t - - {t t}_{11}))]] - - - - - - ((33))$

${u u}_{Cr Cr 11} ((t t)) = = \frac{E E.}{44} cos cos [[{ω ω}_{r r 11} ((t t - - {t t}_{11}))]] - - {Z Z}_{r r 11} {I I}_{b b 11} sin sin [[{ω ω}_{r r 11} ((t t - - {t t}_{11}))]] + + \frac{E E.}{44} - - - - - - ((44))$

S_a1关断瞬间的电压变化率为The voltage change rate at the moment of S _a1 turn-off

${\frac{{du du}_{Sa Sa 11}}{dt dt} | |}_{t t = = {t t}_{11}} = = \frac{{I I}_{b b 11}}{{C C}_{r r 11}}$

(5)(5)

本模式的持续时间为The duration of this mode is

${T T}_{33} = = {t t}_{22} - - {t t}_{11} = = \frac{22 arctan arctan \frac{E E.}{44 {Z Z}_{r r 11} {I I}_{b b 11}}}{{ω ω}_{r r 11}}$

(6)(6)

其中 $ω_{r 1} = \frac{1}{\sqrt{L_{r 1} C_{r 1}}}, Z_{r 1} = \sqrt{\frac{L_{r 1}}{C_{r 1}}} .$ in $ω_{r 1} = \frac{1}{\sqrt{L_{r 1} C_{r 1}}}, Z_{r 1} = \sqrt{\frac{L_{r 1}}{C_{r 1}}} .$

模式4(t₂-t₃)：从t₂时刻开始，L_r1承受的电压值为E/4，L_r1放电，i_Lr1开始从I_b1线性减小，在t₃时刻，当i_Lr1减小到零时，模式4结束。本模式的Mode 4 (t ₂ -t ₃ ): From time t ₂ , the voltage value of L _r1 is E/4, L _r1 discharges, i _Lr1 starts to decrease linearly from I _b1 , at time t ₃ , when i _Lr1 decreases When it reaches zero, mode 4 ends. of this mode

持续时间T₄=T₂。Duration T ₄ =T ₂ .

模式5(t₃-t₄)：辅助电路不工作，正向负载电流I₀通过D₁₃和S₂续流，逆变器工作于稳态。因为在模式4和模式5期间内，u_Cr1等于零，所以S₁在此期间内可以实现零电压开通。本模式持续时间T₅可以根据需要任意设定。Mode 5 (t ₃ -t ₄ ): the auxiliary circuit does not work, the forward load current I ₀ continues to flow through D ₁₃ and S ₂ , and the inverter works in a steady state. Because during mode 4 and mode 5, u _Cr1 is equal to zero, so _S1 can realize zero-voltage turn-on during this period. The duration _T5 of this mode can be set arbitrarily as required.

模式6(t₄-t₅)：在t₄时刻，开通S_a2，同时关断S_a3，在L_r1的作用下，降低了流过S_a2电流的上升率，S_a2实现了零电流开通；因为在关断S_a3之前，流过S_a3的电流已经等于零，所以S_a3实现了零电流关断。开通S_a2以后，L_r1承受的电压值为E/4，L_r1被充电，i_Lr1反向线性增大，在t₅时刻，当i_Lr1反向线性增大到I_b2时，模式6结束。S_a2开通瞬间的电流上升率为Mode 6 (t ₄ -t ₅ ): At time t ₄ , S _a2 is turned on, and S _a3 is turned off at the same time. Under the action of L _r1 , the rate of rise of the current flowing through S _a2 is reduced, and S _a2 realizes zero-current turn-on ;Because before turning off S _a3 , the current flowing through S _a3 is already equal to zero, so S _a3 realizes zero-current shutdown. After S _a2 is turned on, the voltage value of L _r1 is E/4, L _r1 is charged, and i _Lr1 increases linearly in the reverse direction. At time _t5 , when i _Lr1 increases linearly in the reverse direction to I _b2 , mode 6 ends . The current rising rate at the moment of S _a2 turning on

${\frac{{di di}_{Sa Sa 22}}{dt dt} | |}_{t t = = {t t}_{44}} = = \frac{E E.}{44 {L L}_{r r 11}}$

(7)(7)

本模式的持续时间为The duration of this mode is

${T T}_{66} = = {t t}_{55} - - {t t}_{44} = = \frac{44 {L L}_{r r 11} {I I}_{b b 22}}{E E.}$

(8)(8)

模式7(t₅-t₆)：在t₅时刻，关断S₃，在电容C_r1的作用下，降低了S₃关断瞬间端电压的上升率，所以S₃实现了零电压关断。S₃关断以后，L_r1和C_r1开始谐振，L_r1和C_r1被充电，i_Lr1和u_Cr1逐渐增大，当u_Cr1增大到E/4时，i_Lr1反向增加到最大值，然后L_r1开始放电，C_r1继续被充电，i_Lr1开始减小，u_Cr1继续增大。在t₆时刻，当i_Lr1反向减小到I_b2，u_Cr1增大到E/2时，模式7结束。本模式中，i_Lr1和u_Cr1的表达式分别为Mode 7 (t ₅ -t ₆ ): At time t ₅ , S ₃ is turned off, and under the action of capacitor C _r1 , the rising rate of the terminal voltage of S ₃ at the moment of turn-off is reduced, so S ₃ realizes zero-voltage turn-off . After S ₃ is turned off, L _r1 and C _r1 start to resonate, L _r1 and C _r1 are charged, i _Lr1 and u _Cr1 gradually increase, when u _Cr1 increases to E/4, i _Lr1 reversely increases to the maximum value , then L _r1 begins to discharge, C _r1 continues to be charged, i _Lr1 begins to decrease, and u _Cr1 continues to increase. At time t ₆ , when i _Lr1 reversely decreases to I _b2 and u _Cr1 increases to E/2, mode 7 ends. In this mode, the expressions of i _Lr1 and u _Cr1 are respectively

${i i}_{Lr Lr 11} ((t t)) = = (({I I}_{00} {- - I I}_{b b 22})) cos cos [[{ω ω}_{r r 11} ((t t - - {t t}_{55}))]] - - \frac{E E.}{44 {Z Z}_{r r 11}} sin sin [[{ω ω}_{r r 11} ((t t - - {t t}_{55}))]] - - {I I}_{00} - - - - - - ((99))$

${u u}_{Cr Cr 11} ((t t)) = = {Z Z}_{r r 11} (({I I}_{b b 22} - - {I I}_{00})) sin sin [[{ω ω}_{r r 11} ((t t - - {t t}_{55}))]] - - \frac{E E.}{44} cos cos [[{ω ω}_{r r 11} ((t t - - {t t}_{55}))]] + + \frac{E E.}{44} - - - - - - ((1010))$

S₃关断瞬间的电压变化率为The voltage change rate of S ₃ at the moment of turning off

${\frac{{du du}_{S S 33}}{dt dt} | |}_{t t = = {t t}_{55}} = = \frac{{I I}_{b b 22} - - {I I}_{00}}{{C C}_{r r 11}}$

(11)(11)

本模式的持续时间为The duration of this mode is

${T T}_{77} = = {t t}_{66} - - {t t}_{55} = = \frac{22 arctan arctan \frac{E E.}{44 {Z Z}_{r r 11} (({I I}_{b b 22} - - {I I}_{00}))}}{{ω ω}_{r r 11}}$

(12)(12)

模式8(t₆-t₇)：在t₆时刻，D_a1开始导通，此时开通S_a1，则S_a1实现了零电压开通。D_a1导通以后，L_r1承受电压值为E/4，i_Lr1开始反向线性减小。当i_Lr1线性减小到负载电流值I₀时，D_a1截止，S_a1开始导通，i_Lr1继续反向线性减小。在t₇时刻，当i_Lr1反向线性减小到零时，模式8结束，本模式的持续时间T₈=T₆。至此，开关状态b到开关状态a的换流过程结束。其他开关状态之间的换流过程与上述过程类似，这里不再详述。Mode 8 (t ₆ -t ₇ ): at time t ₆ , D _a1 starts to conduct, at this time S _a1 is turned on, and S _a1 realizes zero-voltage turn-on. After D _a1 is turned on, the withstand voltage value of L _r1 is E/4, and i _Lr1 starts to decrease linearly in reverse. When i _Lr1 linearly decreases to the load current value I ₀ , D _a1 cuts off, S _a1 starts to conduct, and i _Lr1 continues to decrease linearly in reverse. At time t ₇ , when i _Lr1 decreases linearly in reverse to zero, mode 8 ends, and the duration of this mode is T ₈ =T ₆ . So far, the commutation process from switching state b to switching state a ends. The commutation process between other switching states is similar to the above process, and will not be described in detail here.

三、软开关的实现条件3. Realization conditions of soft switching

根据以上分析可以得到如下的软开关实现条件：According to the above analysis, the following soft switching realization conditions can be obtained:

①为保证S_a2和S_a3实现零电流开通，其开通瞬间的电流变化率应不大于允许值A，即① In order to ensure that S _a2 and S _a3 realize zero-current turn-on, the current change rate at the moment of turn-on should not be greater than the allowable value A, that is

${\frac{{di di}_{Sa Sa 22}}{dt dt} | |}_{t t = = {t t}_{44}} = = {\frac{{di di}_{Sa Sa 33}}{dt dt} | |}_{t t = = {t t}_{00}} = = \frac{E E.}{44 {L L}_{r r 11}} \leq \leq A A$

(13)(13)

②为保证S_a1和S₃实现零电压关断，其关断瞬间的电压变化率应不大于允许值B，即② In order to ensure that S _a1 and S ₃ realize zero-voltage shutdown, the voltage change rate at the moment of shutdown should not be greater than the allowable value B, that is

${\frac{{du du}_{Sa Sa 11}}{dt dt} | |}_{t t = = {t t}_{11}} = = \frac{{I I}_{b b 11}}{{C C}_{r r 11}} \leq \leq B B$

(14)(14)

${\frac{{du du}_{S S 33}}{dt dt} | |}_{t t = = {t t}_{55}} = = \frac{{I I}_{b b 22} - - {I I}_{00}}{{C C}_{r r 11}} \leq \leq B B$

(15)(15)

③为保证主开关S₁实现零电压开通，其开通时刻相比于硬开关逆变器要滞后时间t_d，使u_Cr1下降到零以后，开通S₁，所以要满足T₂+T₃≤t_d，即③In order to ensure that the main switch S ₁ realizes zero-voltage turn-on, its turn-on time is delayed by t _d compared with the hard-switching inverter, so that S ₁ is turned on after u _Cr1 drops to zero, so T ₂ +T ₃ ≤ t _d , ie

$\frac{44 {L L}_{r r 11} {I I}_{b b 11}}{E E.} + + \frac{22 arctan arctan \frac{E E.}{44 {Z Z}_{r r 11} {I I}_{b b 11}}}{{ω ω}_{r r 11}} \leq \leq {t t}_{d d}$

(16)(16)

④为保证S_a1实现零电压开通，从S₃关断到S_a1开通的间隔时间t_a应不小于T₇，使u_Cr1增大到E/2以后，开通S_a1，所以要满足下式：④ In order to ensure that S _a1 realizes zero-voltage turn-on, the interval time t a from S ₃ turning off to S _a1 turning on _should not be less than T ₇ , so that S _a1 is turned on after u _Cr1 increases to E/2, so the following formula should be satisfied :

$\frac{22 arctan arctan \frac{E E.}{44 {Z Z}_{r r 11} (({I I}_{b b 22} - - {I I}_{00}))}}{{ω ω}_{r r 11}} \leq \leq {t t}_{a a}$

(17)(17)

为在全负荷范围内都可以实现软开关，当负载电流I₀取最大值和最小值时，参数值L_r1、C_r1、I_b1和I_b2的选取应满足式(13)至式(17)。In order to achieve soft switching in the full load range, when the load current I ₀ takes the maximum and minimum values, the selection of parameter values L _r1 , C _r1 , I _b1 and I _b2 should satisfy formula (13) to formula (17 ).

四、辅助谐振电路的逻辑控制Fourth, the logic control of the auxiliary resonant circuit

以开关状态b到开关状态a的换流过程为例，如图3所示，当三电平逆变器主开关要改变开关状态时，相比于硬开关逆变器，主开关的切换要滞后一定的时间T₂+T₃，使u_Cr1下降到零以后，完成主开关的切换。在主开关原动作时刻t₀，关断S_a2，同时开通S_a3，经过时间T₂，当检测到i_Lr1上升到I_b1时，关断S_a1。然后再经过时间T₃，当检测到u_Cr1下降到零时，开通主开关S₁。S₁开通以后，经过时间T₄+T₅，开通S_a2，同时关断S_a3，然后再经过时间T₅，当检测到i_Lr1反向上升到I_b2时，关断主开关S₃。然后再经过时间T₇，当检测到u_Cr1增大到E/2时，开通S_a1。根据式(2),(6),(8)和(12)，可以计算出以上的控制时间，为方便控制，当参数值L_r1、C_r1、I_b1和I_b2确定以后，取I₀为最大值，来计算T₇，这样以上各控制时间都是固定值，不随负载电流变化，所以辅助谐振电路可以采用固定时间控制。Taking the commutation process from switching state b to switching state a as an example, as shown in Figure 3, when the main switch of the three-level inverter needs to change the switching state, compared with the hard-switching inverter, the switching of the main switch takes longer Delay a certain time T ₂ +T ₃ , and after u _Cr1 drops to zero, the switching of the main switch is completed. At the original action time t ₀ of the main switch, S _a2 is turned off, and S _a3 is turned on at the same time. After time T ₂ , when it is detected that i _Lr1 rises to I _b1 , S _a1 is turned off. Then after time T ₃ , when it is detected that u _Cr1 drops to zero, the main switch S ₁ is turned on. After S ₁ is turned on, after time T ₄ +T ₅ , S _a2 is turned on, and S _a3 is turned off at the same time, and after time T ₅ , when it is detected that i _Lr1 reversely rises to I _b2 , main switch S ₃ is turned off. Then after time T ₇ , when it is detected that u _Cr1 increases to E/2, S _a1 is turned on. According to formulas (2), (6), (8) and (12), the above control time can be calculated. For the convenience of control, when the parameter values L _r1 , C _r1 , I _b1 and I _b2 are determined, take I ₀ T ₇ is calculated as the maximum value, so that the above control times are all fixed values and do not change with the load current, so the auxiliary resonant circuit can be controlled by a fixed time.

五、实验结果5. Experimental results

根据图1制作了功率3kW实验样机，三相阻感性负载接在逆变器输出端。实验电路参数值如下：输入直流电压E=200V，最大输出电流I_0peak=14A，谐振电流设定值I_b1=I_b2=20A，输出功率P₀=3kW，直流侧电容C₁=C₂=C₃=C₄=5600μF，谐振电感L_r1=L_r2=20μH，谐振电容C_r1=C_r2=200nF，负载电感L_a=L_b=L_c=1mH，负载电阻R_a=R_b=R_c=10Ω，输出频率f₀=50Hz，开关频率f_c=10kHz。将参数值代入式(13),(14),(15),(16)和(17)中，可以验证参数满足要求。According to Figure 1, the experimental prototype with a power of 3kW was made, and the three-phase resistive and inductive load was connected to the output end of the inverter. The parameters of the experimental circuit are as follows: input DC voltage E=200V, maximum output current I _0peak =14A, resonant current setting value I _b1 =I _b2 =20A, output power P ₀ =3kW, DC side capacitance C ₁ =C ₂ = C ₃ =C ₄ =5600μF, resonant inductance L _r1 =L _r2 =20μH, resonant capacitor C _r1 =C _r2 =200nF, load inductance L _a =L _b =L _c =1mH, load resistance R _a =R _b =R _c =10Ω, output frequency f ₀ =50Hz, switching frequency f _c =10kHz. Substituting parameter values into equations (13), (14), (15), (16) and (17) can verify that the parameters meet the requirements.

谐振电容C_r1的端电压u_Cr1和谐振电流i_Lr1的实验波形如图5(a)所示，u_Cr1的波形出现了零电压凹槽，所以三电平逆变器的主开关可以在零电压条件下完成切换。S_a1开通和关断时的电压u_Sa1和电流i_Sa1的实验波形如图5(b)所示，S_a1开通时，端电压u_Sa1先降到零，然后电流i_Sa1开始上升，S_a1实现了零电压开通；S_a1关断时，u_Sa1以较低的变化率增大，S_a1实现了零电压关断。S_a2开通和关断时的电压u_Sa2和电流i_Sa2的实验波形如图5(c)所示，S_a2开通时，i_Sa2以较低的变化率反向增大，S_a2实现了零电流开通；S_a2关断时，i_Sa2已经先下降到零，S_a2实现了零电流关断。S_a3开通和关断时的电压u_Sa3和电流i_Sa3的实验波形如图5(d)所示，S_a3开通时，i_Sa3以较低的变化率增大，S_a3实现了零电流开通；S_a3关断时，i_Sa3已经先减小到零，S_a3实现了零电流关断。在输出频率为50Hz时，三电平逆变器输出的线电压u_ab的实验波形和三相输出的相电流i_a，i_b和i_c的实验波形分别如图5(e)和图5(f)所示，可以看出逆变器输出的线电压和相电流的波形无明显畸变，辅助谐振电路对逆变器的输出无明显影响，逆变器的输出可以被很好地控制。为验证本发明三电平软开关逆变器在效率上的优势，在相同实验条件下对三电平软开关逆变器和和三电平硬开关逆变器进行了效率测试，在输出功率3kW时，软开关逆变器的实测效率达到96.2%，相比于硬开关逆变器，效率提高2.6%。The experimental waveforms of the terminal voltage u _Cr1 of the resonant capacitor C _r1 and the resonant current i _Lr1 are shown in Figure 5(a). The waveform of u _Cr1 has a zero voltage groove, so the main switch of the three-level inverter can Switching is done under voltage conditions. The experimental waveforms of voltage _{u Sa1} _and _current _i _Sa1 when S _a1 is turned on and off are _shown in Fig. 5(b). Realized zero-voltage turn-on; when S _a1 is turned off, u _Sa1 increases with a lower rate of change, and S _a1 realizes zero-voltage turn-off. The experimental waveforms of voltage _{u Sa2} _and current i _Sa2 when S _a2 is turned on and off _are shown in Fig _. 5(c). The current is turned on; when S _a2 is turned off, i _Sa2 has dropped to zero first, and S _a2 has achieved zero current turn-off. The experimental waveforms of voltage u _Sa3 and current i _Sa3 when S _a3 is turned on and off are shown in Fig. 5(d). When S _a3 is turned on, i _Sa3 increases at a lower rate of change, and S _a3 realizes zero current turn-on ; When S _a3 is turned off, i _Sa3 has been reduced to zero first, and S _a3 has achieved zero current shutdown. When the output frequency is 50Hz, the experimental waveforms of the line voltage u _ab output by the three-level inverter and the phase currents i _a , i _b and i _c of the three-phase output are shown in Fig. 5(e) and Fig. 5 respectively As shown in (f), it can be seen that the waveforms of the line voltage and phase current output by the inverter have no obvious distortion, the auxiliary resonant circuit has no obvious influence on the output of the inverter, and the output of the inverter can be well controlled. In order to verify the advantages of the efficiency of the three-level soft-switching inverter of the present invention, the three-level soft-switching inverter and the three-level hard-switching inverter were tested for efficiency under the same experimental conditions. At 3kW, the measured efficiency of the soft-switching inverter reaches 96.2%, which is 2.6% higher than that of the hard-switching inverter.

Claims

1. A resonant DC link three-level soft-switching inverter circuit, its main circuit includes a DC power supply (1), a diode-clamped three-phase three-level pulse width modulation inverter (3) and three-phase The resistive inductive load (4) is characterized in that: in the auxiliary resonant circuit (2) added in the DC link, there are four electrolytic capacitors with voltage dividing function, six auxiliary switches, six diodes, two resonant capacitors and two a resonant inductor; four electrolytic capacitors C ₁ , C ₂ , C ₃ and C ₄ are connected in series between the DC bus bars, and auxiliary switches S _{a 1} , S _{a 2} , S _{a 3} , S _{a 4} , S _{a 5} and S Diodes D _{a 1} , D _{a 2} , D _{a 3} , D _{a 4} , D _{a 5} and D _{a 6} are connected in antiparallel to _{a 6} respectively; the cathode of diode D _{a 1} is connected to the P1 pole of the DC bus, and the anode of diode D _{a 1} It is connected to the P2 pole of the DC bus, the collector of the switching device S _{a 1} is connected to the cathode of the diode D _{a 1} , the emitter of the switching device S _{a 1} is connected to the anode of the diode D _{a 1} , and the emitter of the switching device S _{a 2} It is connected to the P2 pole of the DC bus, the anode of the diode D _{a 2} is connected to the emitter of the switching device S _{a 2} , the cathode of the diode D _{a 2} is connected to the collector of the switching device S _{a 2} , and the collector of the switching device S _{a 2} Connected to the collector of switching device S _{a 3} , the cathode of diode D _{a 3} is connected to the collector of switching device S _{a 3} , the anode of diode D _{a 3} is connected to the emitter of switching device S _{a 3} , the emitter of S _{a 3} The pole is connected to one end of the resonant inductance L _{r 1} , the other end of the resonant inductance L _{r 1} is connected to the positive pole of the electrolytic capacitor C ₂ , the positive pole of the electrolytic capacitor C ₂ is connected to the negative pole of the electrolytic capacitor C 1, and the positive pole of the electrolytic capacitor C ₁ is connected to the negative pole of the electrolytic capacitor C ₁ The P1 pole of the DC bus is connected; the cathode of the diode D _{a 4} is connected with the N2 pole of the DC bus, the anode of the diode D _{a 4} is connected with the N1 pole of the DC bus, the collector of the switching device S _{a 4} is connected with the cathode of the diode D _{a 4} The emitter of switching device S _{a 4} is connected with the anode of diode D _{a 4} , the emitter of switching device S _{a 6} is connected with the N2 pole of the DC bus, and the anode of diode D _{a 6} is connected with the emitter of switching device S _{a 6} connected, the cathode of diode D _{a 6} is connected to the collector of switching device S _{a 6} , the collector of switching device S _{a 6} is connected to the collector of switching device S _{a 5} , the cathode of diode D _{a 5} is connected to the collector of switching device S _{a 5} The collector of the diode D _{a 5} is connected to the emitter of the switching device S _{a 5} , the emitter of the switching device S _{a 5} is connected to one end of the resonant inductor L _{r 2} , the other end of the resonant inductor L _{r 2} is connected to the electrolytic The positive pole of the capacitor C4 is _{connected, the positive pole of the electrolytic capacitor C4} _is _connected with the negative pole of the electrolytic capacitor C3 , and the electrolytic capacitor C The positive pole of ₃ is connected to the negative pole of the electrolytic capacitor C2 , the negative pole of the electrolytic capacitor C4 is connected to the N1 pole of the DC bus bar; one _end of the resonant capacitor C _{r 1} _is connected to the P2 pole of the DC bus bar, and the other end of the resonant capacitor C _{r 1} is connected to the pole of the DC bus bar One end of the resonant capacitor C _{r 2} is connected, the other end of the resonant capacitor C _{r 2} is connected to the N2 pole of the DC bus, and the connection point of the resonant capacitor C _{r 1} and the resonant capacitor C _{r 2} is connected to the electrolytic capacitor C ₂ and the electrolytic capacitor C ₃ The P1 pole of the DC bus is connected to the positive pole of the DC power supply, the P2 pole of the DC bus is connected to the positive terminal of the inverter bridge, the N1 pole of the DC bus is connected to the negative pole of the DC power supply, and the N2 pole of the DC bus is connected to the inverter bridge. The negative terminal of the transformer bridge is connected.